The Living Abyss
by Nacrene
Summary: The Doctor, Ian, Barbara and Susan have landed in a Hydrea, a vast, technologically advanced city at the bottom of the Atlantic in Earth's distant future with gorgeous views of the ocean outside. A perfect place to rest, and nosy some laboratories, perhaps - or is there something more sinister going on? A season 1 episode set between the Keys of Marinus and the Aztecs.
1. Part 1: Hydrea

**Part 1**

Barbara had never seen anything quite like it. The TARDIS had landed in an enormous glass dome, with corridors connecting from all directions to what she could see through the glass was a cluster of other domes, some transparent and some opaque. Beyond this cluster, more clusters of domes were apparent, stretching as far as she could see.

This wasn't what really grabbed her attention, however. Regardless of how magnificent the domes stretching ahead of them appeared, they were nothing compared to the vast, colourful darkness surrounding them. Strange creatures swam past the dome, some appearing to be ordinary fish, and others a variety of shapes, glowing a spectrum of colours, looking for all the world like creatures from another planet. Which was, Barbara reminded herself, entirely within the realm of possibility.

Susan and Ian followed her out, and she heard Susan gasp behind her.

"Doctor, come and see this," Ian called.

They could hear the Doctor grumbling inside the blue box, still trying to get the scanner to work. Apparently conceding defeat – for now, at least - the Doctor strode out of the TARDIS. His irritated expression vanished, and eyes gleamed as he surveyed the domes ahead of them, appearing far more interested in them than the ocean around them.

"My word," he said. "I do believe we are underwater, in some form of city."

It seemed a reasonable deduction, but, gazing at the creatures outside the window, one question persisted in Barbara's mind.

"Are we on Earth?" she asked.

"What sort of a question is that?"

They jumped and turned. A young man, who must have only been in his twenties, was standing behind them, a look of bemusement on his face. His dress was very ordinary, even casual, but he had some sort of technology, like half a pair of glasses, hooked over his ear and in front of his eye.

"Are you from off-world?" he asked.

"That depends, my child," said the Doctor. "Where are we?"

The man gave them another confused look, and Ian coughed.

"Our ship isn't exactly… accurate," he ventured.

"Nonsense," snapped the Doctor. "The scanner needs repairs, that's all."

"You're on Earth," said the young man, eventually. "In Hydrea." He paused, before adding, almost as an afterthought, "At the bottom of the Atlantic." He looked over the TARDIS. "Is that your ship? Why does it look like a phone box?"

"Well, it's a disguise," said Susan.

"It's not a very good one," said the man. "How did you all fit in there?"

"Never you mind," said the Doctor, who had been growing more and more irritated with the conversation as it went on. "I must see more of this city. Where do you get your energy from, mm?"

"Here, actually," said the man. "We're a geothermal power plant. We generate energy from the Mid-Atlantic Ridge."

The gleam returned to the Doctor's eyes. "Fascinating," he said. "You must take me to see your laboratories."

"Do you think they might have some materials you can use to repair the scanner?" asked Ian.

"An excellent point," said the Doctor. "We shall see."

The man stared, stunned, his mouth opening and closing. "Sorry," he said, getting a handle on his vocal chords, "I'm just an intern, I don't actually…"

"Theodore!"

This time, it was the man's turn to jump and turn. A man and a woman, both wearing lab coats with their sleeves rolled up, came in from the corridor behind the TARDIS. The woman hurried over to the young man.

"Theodore," she repeated, "who are these people?"

"And why is there a phone booth parked in the observation dome?" asked the man.

"Sorry, sorry," said Theodore, rubbing his temples. "These are some… travellers. I think they're from off-world. They say their ship -" he indicated the TARDIS "- is broken down."

"We said nothing of the sort," said the Doctor.

Barbara stepped forwards. "We're terribly sorry," she said. "We'll move our ship as soon as we can. I'm Barbara, these are Ian, Susan and the Doctor."

"I'm Yandi, this is Reina," said the man. "I'm the head of this facility. I really must insist that you remove your… ship… immediately."

"Hmph," said the Doctor. "I'm afraid we can't move it just yet."

Ian and Barbara exchanged a glance. It was impossible to tell whether the old man was telling the truth or not, especially after the Dalek fiasco.

"Why not?" said Yandi.

"Because their ship is broken down?" Theodore volunteered.

"It is _not, not_ broken," the Doctor repeated. "But the scanner needs to be repaired. We ought not land anywhere without the ah, the ability to see where we are. We were lucky this time, but who knows where we might end up next."

"I could have you arrested for causing an obstruction," Yandi warned.

" _Really_ now," said Reina, under her breath.

"If you arrest us," said Ian, "nobody will be able to remove the ship."

"We could remove it forcibly," Yandi said.

Susan stifled a laugh. Yandi narrowed his eyes.

"Very well," he said. "We'll help you, if we can. What do you need?"

The Doctor's face broke into a wide smile. "Take me to your laboratories," he said. "If there is anything of use there, I will tell you."

Yandi waved his hand tiredly. "Very well," he said. "But we will only take two of you. The other two can wait in the cafeteria."

"Susan and I can wait," Barbara volunteered. "I'd rather sit and look at the ocean, anyway."

"Excellent. Chesterton, you will accompany me," said the Doctor. He turned to Yandi. "Lead the way."

"Theodore, take the women to the cafeteria," sighed Yandi. He jerked his thumb at the Doctor and Ian. "You two, follow us."

It was hard to imagine a better place to have your lunch. The fish weren't that colourful in themselves, that was true, but they made up for it with the lights that covered them from head to tail.

"It's called bioluminescence," Theodore was telling Susan.

"It's beautiful," said Susan, as an enormous eel with lights along its belly swam above them.

They sat around a large table, eating the sandwiches that Theodore had managed to procure for them while they waited. The cafeteria wasn't particularly busy, despite the fact that it was lunch time. It didn't seem that many people working here – but, though Barbara didn't know quite how far into the future they were, she supposed automation must have done away with the need for quite so many workers by now.

"It's nice to be somewhere as lovely as this, for once," Barbara commented.

"Oh, yes," said Susan. "I much prefer this to -" But before she could finish, she cut herself off with a yelp.

"Susan?" Barbara hurried to Susan's side, Theodore close behind. The girl was sitting, clutching her head in agony.

"Barbara, make it stop!"

"What is it, Susan?"

"Can't you hear them?" Susan held her temples, shaking. She looked into Barbara's eyes, her face painted with fear. "Horrible, horrible voices. Can't you feel it? Can't you feel the sadness?"


	2. Part 2: Voices from the Deep

**Part 2**

Barbara held Susan as she shook, her head clutched in her hands.

"Terrible, terrible sadness," Susan murmured faintly.

After a time, she settled, the trembling stopped and Susan sat up again.

"Um," said Theodore. "Are you okay?"

"It stopped," Susan said, "but I can feel it, you know. I can feel something here."

Barbara wondered whether Susan had just had an adverse reaction to an unusually intense headache, but the girl _was_ odd. If there were voices, trying to make themselves heard, then it seemed to Barbara that Susan would likely be the first to hear them.

Theodore didn't seem to agree.

"Was it just a headache?"

"No," said Susan. "I heard voices."

"Perhaps we should tell Ian and the Doctor when they return," said Barbara.

"Is she okay?" asked Theodore, still looking nervously from Barbara to Susan.

"She will be, I'm sure," said Barbara. "Give her time."

"I've been wondering," said Theodore, settling back down now. "Who are you all? You say you came here in a ship that looks, to me, like a phone booth. Phone booths aren't very aerodynamic."

"Oh, it's a long story," said Barbara. "Ian and I started travelling with the Doctor and Susan quite by accident."

"Travelling where?"

"Everywhere," said Barbara, shortly. "And yourself? What's your story, Theodore?"

"You already know, really," said Theodore. "I'm an intern, from England. I came down here to work in the power plant for a year."

"What do you do?"

"This power plant isn't just a power plant," said Theodore. "Lots of scientists live here, studying the ocean. We've got oceanographers, ecologists, physicists, geologists, volcanologists… I'm a geologist."

"Well, you must spend a lot of time in the power plant, then," said Barbara.

"No, not really," said Theodore. "I've not actually been there very often…"

They kept talking, and Barbara learned that Theodore's internship seemed to involve fetching drinks for Yandi more than anything. Shortly afterwards, the Doctor and Ian returned, the Doctor appearing to be deep in thought. Yandi and Reina followed, Yandi continuing to look annoyed. The two scientists went to Theodore and began to speak to him in hushed voices, while the Doctor sat absentmindedly next to Susan.

"He says he might be able to fix the scanner with some of the materials they have here," said Ian, after taking Barbara aside. "But if you ask me, he's more interested in their laboratories than the scanner."

"Well, I'm not surprised," said Barbara. "How long do you think we'll be staying?"

"Yandi's been arguing with him about the materials. He wants us to pay for them, but, well, you know we don't have any money. The Doctor's convinced them to let us stay the night, while we sort it out."

"I won't say no to that," said Barbara. "Though… Susan says she's hearing voices."

"Voices?" said Ian incredulously. "Nonsense. I'm sure she just has a bad headache. There doesn't seem to be -"

Before he could finish, it hit them. The four travellers buckled over, and Barbara could feel an intense ache in her mind. She understood what Susan meant now – they weren't so much _voices_ as they were an unsettling feeling. A sense of deep sorrow.

Susan, whose mind was clearly more sensitive to this sort of thing than the rest of them, was hit the hardest. She fell to the ground, clutching her head once more.

It took a while after it had ended for Barbara to realise that the voices had stopped. She found that she had been instinctively bracing herself for the pain, and the voices faded so gradually that she barely noticed when it was gone.

"Perhaps Susan was right," Ian conceded, quietly, when it had ended.

Yandi appeared to be concerned.

"Are you all right?" he asked.

"I supp- I assume you all felt the same thing?" said the Doctor, looking over at his companions. "We felt some kind of… some kind of a presence."

"I felt it before," added Susan. "Not long ago. Terrible sadness."

"Ah, dear," said Yandi. "Don't worry about that, it's just a side effect of the pressure here, like astronauts getting used to the gravity. You'll be fine in no time. Theodore, they're staying in the guest quarters, why don't you show them to their room?"

"A side effect of the pressure?" said Ian. "That sounds ridiculous!"

"It's true," said Theodore. "They warned me about it before I came down here. I didn't believe them, but it happened to me as well. Humans didn't evolve for these depths, it's just an ordinary reaction."

Yandi nodded. "Don't worry about it," he said. "Once we've figured payment out, you'll be out of here before too long."

He gave the Doctor a pointed look, which the traveller avoided.

Their room was luxurious, with each of them given their own double bed and a bedside table. Bathrobes were folded on the foot of each bed, and a long, curved window on the ceiling gave them all a spectacular view of the ocean above.

"Grandfather," said Susan, once they had settled down and Theodore had left them for the night.

"Yes, my dear?" asked the Doctor, coming to sit down next to his granddaughter.

"Do we have to stay? I don't like it here. Well - I don't like the voices."

"I'm afraid so," said the Doctor. "With the scanner broken, we won't know where we land." He tapped the corner of his mouth. "And something isn't quite right. I _must_ get to the bottom of it."

"Oh, okay." Susan knew that when her grandfather got himself hooked onto a mystery, but when he did it was impossible to make him change his mind.

The Doctor hugged her. "I'm sorry," he said. "We shall only stay for one more day."

The beds were so comfortable that they soon forgot about the voices, or pressure, or whatever it was. Even Susan began to settle down, despite the constant mumbling that she felt, miles away in the back of her mind. At least the mumbling didn't seem to be distressed, not like the voices before. This just felt like… conversation.

It took a while, but eventually they all fell asleep. The base powered down, so that the only light that filtered into the room now was that of animals, flitting over the windows above, and the only sound was the barely perceptible noise of oxygen being pumped around the city

Susan suddenly awoke. For a moment, she thought she had been woken by the voices again, but then she realised that the source of her discomfort was something altogether different.

Before she could scream, there was a hand over her mouth and a low voice hushed her.

"Don't make a fuss," hissed Reina. "When I move my hand, I need you to wake the others – _quietly_. I know you can hear them. I used to hear them too. _I need your help_."


	3. Part 3: Psychic Sponges

**Part 3**

It was difficult, making their way through the laboratories in the darkness. They didn't even have any windows into the ocean to provide bioluminescence, but it was either this or get caught – which, _apparently_ , they didn't want to do. Ian didn't really see an argument with that. The fact that they were sneaking around seemed to support this, at least.

Susan had woken them late at night, accompanied by Reina, who had claimed that the voices they'd heard weren't side-effects of the pressure after all.

Ian was very willing to believe that, but he hadn't been prepared for what Reina claimed was the real reason.

"Psychic sponges."

"What do you mean, psychic sponges?" Ian asked.

"It'll make more sense if I show you," said Reina. "Come with me."

"Hmph," said the Doctor, though his curiosity was written plainly across his face. "And why should we?"

"I need your help," said Reina. "If you help me, I'll help you get the materials to fix your scanner."

This seemed to appease the old man, and he allowed her to lead the way back into the laboratories. She had a dim torch, which she only used when absolutely necessary. Other than that, they were in the dark, half making their way by feel. Reina led them down to the laboratories, and through a series of corridors therein that Ian and the Doctor hadn't even seen during their tour earlier that day.

"Here it is," Reina hissed. "Or, some of it."

She shone her torch on a beaker, filled with some sort of sludge. It pulsed slightly as she moved the light over it.

As she did, Susan doubled over again.

"There it is again!" Susan whispered. "One of the voices."

"Hmm? Hmm!" the Doctor looked over the beaker. "I can feel it too, my child. Not as strongly as you, I think, but you're right."

"What is it?" asked Ian.

"It is as this young lady claims, I believe," said the Doctor. "Psychic sponges, indeed! Hmm! They must have evolved here over millions of years!"

"Why are they psychic?"

"So they can talk to each other!" said Susan. "Am I right, Grandfather? That must be the mumbling I can hear."

"That's what we think," said Reina. "Psychic sponges, they must have evolved sentience, and then psychic abilities to communicate with each other in the depths of the oceans."

"Why are they here?" asked Barbara.

"And why are they sad?" asked Susan.

Reina's expression was grim. "Well, you see, that's the problem. The energy we make in the plant isn't geothermal – it comes from these. We process them."

"That's horrible," gasped Susan.

"Why, that's barbaric!" said Ian.

"It's efficient," said Reina. "And so much of our technology has developed from studying them. Organic computers, efficient, sustainable energy, and psychic shields."

"And why do you need psychic, eh, psychic shields, mm?" asked the Doctor.

"So we don't hear the screaming," said Reina. "Once you're here for a day, you develop psychic shields. When the plant grew into a city, and civilians came down, we made up a lie that the voices were a short-term thing to do with the depths, and, well, people accepted it after a while."

"So why are you telling us all of this?" asked Ian. "What do you want us to do?"

"I want this to stop," said Reina. "Yandi keeps close tabs on me, he won't even let me tell Theodore about it. But I want this to stop." She turned to the Doctor. "You, Doctor, I watched you while we showed you around the lab. You are a man of science. I haven't figured out how to do it, but maybe you can help me."

"Do what, exactly?" said the Doctor.

"Let us talk to the sponges. Not just hear them, _talk_ to them. I want everyone in the city to be able to talk to them. If people find out what is happening, and can talk to them, maybe this will all end."

The Doctor eyed the sponge in the beaker. "Give me some time with it, my girl, and I'll see what I can do."

It became evident, as Ian and the others sat there, watching the Doctor and Reina at work, that he relished the opportunity to work in a laboratory as well equipped as this. They weren't even sure whether half the instruments he was using were actually necessary for whatever he was doing, as after a few moments of fiddling with them he'd set them aside, grumbling to himself all the while. Each time he did this, Reina would raise her eyebrows, mutter something like "I _told_ you we didn't need that," and be ignored. The Doctor avoided even touching the sponge as much as possible, treating the creature with a reverence they'd previously only seen him show towards his granddaughter.

For once, however, Ian found that it seemed the Doctor knew what he was doing. Unlike the irritated mumblings he made whilst trying to get the TARDIS in line, the old man sounded more and more satisfied as he progressed.

Eventually, it appeared that the pair of them had come to some sort of a conclusion. The Doctor straightened, holding the beaker with the sponge in one hand, and a small bottle with their own concoction in the other. He turned to Reina.

"You mentioned some sort of psychic shields," he said. "How do you, eh, activate them?"

"We use a gas we developed from the sponges," said Reina. "It's in the oxygen supply."

Susan looked queasy at the thought, but the Doctor's face cracked into a fiendish smile.

"Excellent," he said. "I'm going to need to use that."

Reina nodded. "The processing room isn't far from here," she said. "Just down this corridor."

And off they went, again, following corridors and passageways through the labyrinthine laboratories. Ian could only hope that one of the others remembered the way back, because he was quickly growing lost.

They finally ended up in a large room, with pipes running across the walls and a glass tank filled with a greenish gas sitting in the centre.

The Doctor set upon the tank, and Reina waved for the others to sit before returning to his side. The pair of them set about mixing the gas in the tank with the concoction in the bottle, drawing it from a tap on the side of the tank. They exchanged a glance with each other, and the Doctor sniffed the gas in his bottle, before turning to the sponge in the beaker, deep in concentration. There was a moment of silence, and then the old man burst into laughter.

"What _is_ he doing?" Barbara asked.

"He's been trying to reverse the process of the psychic shields," said Reina quietly, turning back from helping the Doctor. "Instead of blocking the voices, he wants the gas to amplify them, make the communication go both ways. I think…" she looked at the Doctor, who was staring at the sponge intently.

"Yes, he is, isn't he?" said Susan. "Yes! I can hear it! He's talking to the sponge, isn't he?"

"Well," came a voice from the doorway, "we can't have that, can we?" Yandi stepped in, enraged. "I told you not to cause trouble, Reina."

"I couldn't stand idly by while you – while _we_ committed atrocities," hissed Reina.

Yandi stepped forward, and they could see he had a gun clutched in his hand. "I'm afraid I can't let you do this," he hissed.

The Doctor's eyes scanned the room, taking everything in. He saw the gun in Yandi's hand, saw Ian and Barbara standing up to protect Susan, saw Reina crouch to lunge towards Yandi.

He did the only thing he could.

He stuck his bottle to the tap on the tank, and poured its contents in.

Their world exploded.


	4. Chapter 4: The Mumbling in the Mind

**Part 4**

Having an entire civilization chattering inside your head can be distracting. It was even distracting for Susan, who by this point had grown accustomed to the mumbling in her mind. And they _were_ a civilization. She could hear them, she could _feel_ them in her mind, not just the sadness of the sponges in the laboratory, but the life and energy of those living miles and miles beneath them, and around them, throughout the vast ocean.

It was a strange sensation, and though she had difficulty explaining it the first time she found that, if she'd been asked to explain it now, it would be far trickier. They weren't quite voices, they weren't quite talking, but they _were_ communicating. They were using thought, and feeling, to ask her who she was, to ask whether she was there to help, to ask why she could hear them at all…

Yet, despite the volume of voices now in her mind, it didn't seem to be too much to handle. They fluctuated, reaching out to her and pulling back, but all the time another part of her was still able to process what was happening in the room, in a strange sort of slow-motion, like the power of thought had made the world slow to treacle around her.

Ian and Barbara were standing protectively in front of Susan, Ian trying to stand in front of Barbara as well. The Doctor had his bottle plugged into the tank, and the gas had just mixed and been diffused. Yandi had his gun out, and Reina leapt, seeming to soar through the air at a tectonic speed.

But Yandi didn't shoot. Before Reina tackled him to the ground, moving more out of instinct than anything at this point, he collapsed to his knees and dropped his gun. The last Susan saw of him, before Reina's body completely knocked him out of the way, was Yandi's wide-eyed face, blankly staring at the ground in front of him.

And then, or so it felt, time happened again.

The Doctor dashed over to Ian and Barbara, while Ian went to Reina to help her. She had Yandi pinned to the ground, but the scientist wasn't struggling at all. Susan could see that his face was still blank, but as she watched she saw a deep sadness developing in his expression.

Reina got up and knelt over him, next to Ian.

"I had to," Yandi said in a quiet voice. "Don't you see? I had to."

"And why did you _have_ to, mm, young man?" asked the Doctor.

"So much energy," said Yandi. "I could have started a golden age for humanity! But the screaming, the _endless_ screaming. I had to make it stop."

"You could have made it stop," said Barbara evenly. "But you didn't."

"You know what I mean." Yandi sighed. "I couldn't give up a source of energy and innovation like this. So we designed organic psychic shields. A way to block the voices out. I'd almost forgotten what it sounded like."

"Well, soon, everybody in the city will hear them," said the Doctor. "And then, I think, you shall have to find another source of energy."

"We really did start as a geothermal plant," said Reina. "The sponges we found quite by accident. Most of the geothermal equipment is still working."

The Doctor smiled. "Well then," he said. "It seems that we have, we have done what you asked. And, in exchange?"

Reina looked at Yandi and lifted him up by his arm. He didn't protest, still trembling, his eyes blank save for sadness.

"I don't think he'll be a problem now," she said. "Come, Doctor. I'll get you your equipment, and you can be off."

They followed Reina back through the corridors. Susan was pleased to see that, this time, they didn't have to feel their way through the darkness. As they went through the laboratories, they met with different scientists, and interns, including Theodore, all bleary-eyed, having just been woken by the sound of a city in their mind.

"It's over," said Reina, shortly, as they passed scientists. Some appeared annoyed, others relieved. Theodore was simply confused.

They picked up the equipment the Doctor needed for the TARDIS scanner, and Susan tried her best to explain to Theodore what had happened.

"Psychic sponges?" he repeated. He paused, in thought. "Yes," he said. "They're telling me that's what they are. How odd."

"Well, I shouldn't think you'll be able to speak with them for much longer," said Susan. "Grandfather just made a short term solution. Enough to stop you hurting them."

Theodore nodded. "I can't believe we… I… a side-effect of the pressure? I can't be that gullible."

"You weren't, at first," said Reina.

"No, indeed," said the Doctor. "There was some kind of a, of a drug in the gas, wasn't there? To make them complacent, hmm?"

Reina nodded. "Yes. It took a lot out of me to fight that. I'm glad you all came when you did."

By this point, they had returned to the TARDIS.

"I tried to get in, you know," said Yandi. Susan jumped slightly. She'd forgotten he was there at all. "I couldn't open it at all."

The Doctor tapped the side of his nose. "Well, of course not," he said. "This is the safest ship in the universe."

Ian and Barbara exchanged a conspiratorial smile. The Doctor harrumphed, slipped his key into the lock, and opened the door. They stepped inside, and Susan giggled at the scientists' expressions.

"Don't worry," she said. "You'll figure it out."

Barbara stayed outside for a few moments, while the Doctor tinkered with the scanner in the TARDIS.

"What will you do now?" she asked Reina.

"Make sure people know," said Reina. "Though I'm sure they're starting to, now. Switch back to geothermal energy, and, well… I can't lead this institution by myself, but I don't think Yandi is suited for it, either. I'll do what I can."

Barbara smiled. "Well, I wish you the best."

"Oh, Barbara!" called Ian's voice from inside the TARDIS. "We're ready!"

Barbara sighed and looked at the ocean around her once more.

"You know," she said, "it really would be nice to go somewhere peaceful, for once."

"I still don't understand," Theodore said. "Where do you travel? How does that ship _work_."

"Do you know, I haven't the faintest idea," said Barbara. "And between you and me, I don't think the Doctor knows either." She stepped into the TARDIS. "But if you're confused _now_ , well… just look at this."

And she closed the door.

The light on the blue box began to flash, and it made a wheezing sound as it gradually faded from view. The scientists goggled at the phone booth, and heard the voices inside growing faint.

"Oh, grandfather," they heard Susan say. "Can we show Barbara and Ian the Rings of Akhaten?"

They heard the Doctor hum and haw, but he was much, much quieter, almost a whisper on the breeze, as he said, "we shall see, my dear. We shall see."


End file.
